Strain insulator



P 1937. L. J. STEVENS 2,093,875 I STRAIN INSULATOR Fiied Dec. 10, 1934 amnion Patented Sept. 21, 1937 UNITEDISTATES STRAIN INSULATOR Leland James Stevens, Baltimore, Md., assignor to Locke Insulator Corporation, Baltimore, Md., a corporation of Maryland Application December 10, 1934, Serial No. 756,885

13 Claims.

The invention relates to strain insulators, that is to say the type in which the dielectric material is maintained under compression and has for its general object the provision of a novel insulator of this variety which is particularly adapted for use in connection with radio equipment either as a primary insulator for directly suspending an antenna, or as a secondary insulator for sectionalizingv guys, though naturally the device is capable of other application.

An importantobject of the invention is to provide a strain insulator which is totally devoid of any hardware fittings of either the clamp type or the cemented type, this being a distinct advantage for operation at radio frequencies.

Another object of the invention is to provide an insulator of this character having maximum mechanical strength combined with minimum weight, and which, electrically considered, will have high flash-over values per inch of striking distance, low capacitance and an unusually long leakage distance.

1 Another object is to provide an insulator of this type of such construction as to permit the ready 2:; employment of preliminarytie means for effecting temporary securing of the insulator prior to the bringing of adequate tension upon it.

I An additional object is to provide a strain insulator having these advantageous characteris- 30 tics and which will at the same time'be simple and inexpensiveto make, easy to install, selfcleaning, positive in action, efficient and durable in service, and a general improvement in the art.

To the attainment of theforegoing and other 35 objects and advantages, the invention preferably consists in the details of construction and the arrangement and combination of parts to be hereinafter more fully described and claimed, and illustrated in the accompanying drawing in 40 which:

Figure l is a side elevation of the insulator,

Figure 2 is an elevation taken at right angles to Figure 1,

Figure 3 is a cross section taken on the line 45 3-3 of Figure 2,

Figure 4 is a cross section taken on the line 4-4 of Figure 2. I

Referring more particularly to the drawing, the insulator is represented as comprising a single dielectric body designated as a whole by the numeral l0 and formed of any suitable material but preferably porcelain and which may be cast or molded, cut or formed in any manner known to the trade, the surfaces being moreover glazed in the well known and usual manner.

Morespecifically, the insulator is represented as including an elongated central or shank portion ll merging at its ends into right angularly disposed arms I2, the device being consequently somewhat T-shaped when viewed from any side. 5 The shank portion II is preferably of cylindrical form in cross section with'radially extending webs or ribs I3 projecting therefrom and merging into the arms l2. At their juncture with the shank II the cross arms l2 are enlarged or formed with 10 spaced substantially circular ribs M which merge into or constitute continuations of the radial webs l3 and which define grooves [5 for the reception of conductors or guy cables as the case may be. At their ends the arms 12 are formed with transl5 verse grooves iii of curved shape which are likewise engageable by the cables for spreading the same.

Another feature is the provision of means enabling the insulator to be temporarily anchored 20 or secured with respect to the cables to be held prior to the application of the final tension thereto. In carrying out this feature I provide each of the arms l2 with transversely: extending holes I! and also providetheir ends with grooves I8 intersecting the seatsl 6, these holes and grooves being designed for the reception-of cords or the like which may be tied about the cables for accomplishing the holding action, the intention being that such cords are to be cut away and discarded after the cables are tightened.

In order to increase the leakage distance between the ends of the arms I 2, I provide on each arm a plurality of corrugations or outwardly projecting ribs l9 located outwardly of the ribs I4 which define the cable seats IS.

The insulator is used in the same manner and for the same purpose as other insulators of the guy strain type, in that each cable is engaged within the grooved seat IS in one cross arm l2 and within the grooves IS in the ends of the other cross arm, the cablesthus interlinking and providing a support for Whatever structure with which it is associated in the event of destruction of the insulator. In so far as actual assembly or installation is concerned, it is clear that the necessary loops could be preformed in the cables and the insulator then inserted in place or, if preferred, the cables can be properly positioned with respect to the insulator and then formed with the necessary loops.

The provision of the radial webs [3 which project outwardly from the elongated central portion or shank II in the plane of greatest strain renders the insulator very strong and gives it the maximum resistance to mechanical shock as well as enabling it to withstand high compressive strain, the ultimate strength in pounds necessarily depending upon the dimensions though a comparatively small insulator constructed in this manner has been found to possess such strength as to withstand a strain of 30,000 pounds. From the electrical viewpoint the insulator performs remarkably satisfactorily as there is an unusually long leakage distance which is of course measured between the grooves l5 and 16. Tests have.

indicated that an insulator of this construction capable of withstanding 30,000 pounds strain has a sixty cycle dry arc-over voltage of 50,000 volts, thus making the insulator eminently suitable for use in radio transmission. Another feature is that as there are no hidden surfaces the insulator is not only self-cleaning when rained upon but will become wet all over, thereby equalizing electrostatic stresses. Owing to the peculiar shape the mass of the insulator is relatively. small so that there will be low capacitance. This feature combined with the absence of metallic fittings of any type additionally renders the device suitable as a primary insulator for supporting a radio antenna or as a secondary insulator disposable in the guys of an aerial mast or the like. It has been found in service that insulators constructed in this manner are especially suitable for use" on ship installations or under other conditions where excessive whipping of an antenna may be expected.

From the above it is believed that the construction, use and advantages will be readily apparcut to one skilled in the art without further explanation.

While I have shown and described the preferred embodiment of the invention and have illustrated certain proportions and shape of the parts, it should be understood that I reserve the right to make all such changes in these details as will constitute no departure from the spirit of the invention or the scope of the claims hereunto appended.

Having thus described the invention, I claim:

1. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at an angle to eachother and each formed with grooves in the ends and at the center, the central groove in each arm being in the same plane as the grooves in the ends of the other arm.

2. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at an angle to each other and each formed with grooves in the ends and at the center, the central groove in each arm being in the same plane as the grooves in the ends of the other arm, said body being substantially cruciform in cross section.

3. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at an angle to each other and each formed with grooves in the ends and at the center, the central groove in each arm being in the same plane as the grooves in the ends of the other arm, both ends being duplicates.

4. A strain insulator comprising an elongated body of dielectric material provided at its ends with laterally extending arms arranged at right angles to each other, said body having radially extending webs merging into said arms, said arms being provided centrally and at their ends with cable receiving grooves, the central groove in each arm lying in the same plane as the grooves in the ends of the other arm.

5. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extending arms whereby the insulator will be of substantially T-shape in side elevation, the arms at one end being at right angles to those at the other end, said body having radially extending webs merging into the arms, said armshaving their ends formed with cable receiving grooves and being formed centrally with grooves defined between ribs merging into and constituting con- .tinuations of said webs, the central groove in each arm and the grooves in the ends of the other arm lying in the same plane.

6. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at an angle to each other and formed with central grooves and with grooves in their ends, the central groove in each arm being in the same plane as the grooves in-the end of the other arm, said arms being additionally provided with means for the reception of temporary securing elements.

'7. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at an angle to each other and formed with central grooves and with grooves in their ends, the central groove in each arm being in the same plane as the grooves in the end of the other arm, said arms being further provided with transverse holes near the end por tions adapted for the reception of temporary tie means.

8. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at right angles to each other and each formed with a central groove and with grooves in its ends, the central groove in each arm being in the same plane as'the grooves in the ends of the other arm, said body being formed with a plurality of longitudinally extending webs connecting the arms.

9. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at substantially right angles to each other, each of said arms being formed centrally with spaced ribs defining a groove and each being provided with grooves in its ends, the central groove in each arm lying in the same plane as the grooves in the ends of the other arm.

10. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at substantially right angles to each other, each of said arms being formed centrally with spaced ribs defining a groove and each being provided with grooves in its ends, the central groove in each arm lying in the same plane as the grooves in the ends of the other arm, and each arm being formed between said ribs and its ends with other ribs for increasing the leakage distance.

11. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extended arms disposed at substantially right angles to each other, each of said arms being formed centrally with spaced ribs defining a groove and each being provided with grooves in its ends, the central groove in each arm lying in the same plane as the grooves in the ends of the other arm, each arm being formed with transverse holes near the ends and further having its ends formed with other grooves at right angles to the first named grooves, said holes and said last named grooves providing for the accommodation of temporary tie means.

12. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extending arms disposed at right angles to each other and each formed with a central groove and with grooves in its ends, the central groove in each arm being in the same plane as the grooves in the ends of the other arm.

13. A strain insulator comprising an elongated dielectric body provided at its ends with laterally extending arms disposed at an angle to each other and each formed with wire receiving passages in the ends and at the center, the central passage in each arm being in the same plane as the passages in the ends of the other arm.

LELAND JAMES STEVENS. 

